JP2019107684A - Cast piece molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slab forming method capable of reducing the width dimension of a slab whose width dimension is determined by a mold dimension of a continuous casting machine while suppressing the occurrence of seam flaws on the surface layer of the slab. SOLUTION: In a slab forming method, a slab is pressed once or more in the width direction by a first die while changing the relative position of the slab and the first die in the longitudinal direction. , The first parallel portion by the second mold while changing the relative position in the longitudinal direction between the slab and the second mold in the first press process for forming the first inclined portion and the first parallel portion. It has a second pressing step of forming a second inclined portion and a second parallel portion by pressing a part of the slab in the width direction of the slab one or more times, and is the first in the first pressing step. The relationship between the total width reduction amount Rα, which is the reduction amount of one parallel portion, and the total width reduction amount Rβ, which is the reduction amount of the second parallel portion in the second pressing step, is Rα / Rβ ≦ 0.7 or Rα. Press so that / Rβ ≧ 2.0. [Selection diagram] FIG. 8

Description

  The present invention relates to a method for forming a slab for reducing the width dimension of a slab to a desired size.

  In recent years, the quality and the size of the steel plate required have been diversified, reflecting the tendency of diversification of industrial products, and in particular, the product sizes required for the steel plate are extremely diversified.

  Generally, in order to manufacture a steel plate of a predetermined size, it is necessary to prepare a cast of a size suitable for the size. However, when using a slab obtained from a continuous casting machine, the width dimension of the slab is determined depending on the size of the mold of the continuous casting machine, so it is difficult to make separate slabs of optimal width dimensions for each product .

  Therefore, as described in Patent Documents 1 and 2, the product thickness of the cast slab is different from that of the cast slab in order to make the cast slab having a predetermined width obtained by the continuous casting machine with the optimal width dimension for each product. Before horizontal rolling by horizontal rolls in the thickness direction, width rolling (sizing mill rolling method) using a crucible roll is performed.

  When width rolling is performed, an increase in thickness (dog bone) in the thickness direction is formed at the widthwise end of the cast slab. Then, by horizontally rolling this thickness-increasing part, a concave shape called a fishtail is formed at the longitudinal direction end of the cast slab. Since this fishtail is cut off and becomes scrap, there is a problem that the yield is lowered.

  In order to solve this problem, as shown in FIG. 1, a sizing mill rolling method has been conventionally employed in which width rolling is performed using a crucible roll 100 having caliber portions 101 at both ends in the rotational axis direction. When such a skewer roll 100 is used, the increase in the thickness dimension of the thickness-increasing portion can be suppressed by the caliber portion 101, so that the fishtail can be made smaller.

  However, providing the caliber portion 101 on the skewer roll 100 is insufficient as a measure to reduce the fish tail. Therefore, as a technology to make the fish tail smaller, a sizing press rolling method has been developed in which a cast strip is subjected to width reduction using a mold.

  In the sizing press reduction method, it is possible to suppress the thickness increase at the width direction end of the slab during width reduction, and it is difficult to produce a fish tail. However, performing the width reduction over the entire length in the longitudinal direction of the slab by the sizing press reduction method alone is inferior in productivity to the case of employing the sizing mill rolling method.

  Therefore, in Patent Document 3, only the longitudinal end (front and rear ends) of the cast slab where the fish tail becomes a problem is width-reduced by the sizing press reduction method, and the other longitudinal center portion is the sizing mill using a skewer roll. By performing width rolling by a rolling method, a technology for achieving both high yield and productivity has been proposed.

  If the width of the longitudinal end of the slab after width reduction by the sizing press method is larger than the width rolled by the sizing mill method, a fish tail will be produced. In order to prevent this, it is conceivable to increase the reduction amount in the sizing press reduction method. However, if the amount of reduction by the sizing press reduction method becomes large, the contact area between the slab and the mold becomes large, and a robust equipment equipped with a mold that can withstand the reaction force during the reduction is required, which is uneconomical .

  Therefore, according to Patent Document 4, the casting can be performed as a method for reducing the width of a slab that enables large reduction of the longitudinal end of the slab while suppressing the equipment cost, and that can also be operated to secure productivity. After forming an oblique side portion which is contracted from the base side to the front side and the rear side of the piece and a preliminary parallel portion which is connected thereto and longer than the length of the oblique side portion, There has been proposed a method of forming a new oblique side portion and a parallel portion by moving in the reverse direction and further pressing the part except at least a part on the base side of the preliminary parallel portion with a pair of dies.

Japanese Patent Application Laid-Open No. 60-106601 Japanese Patent Application Laid-Open No. 62-97701 JP 2008-254048 A JP 2008-254034 A

As described above, according to the techniques described in Patent Documents 3 and 4, the sizing mill rolling with high productivity is performed while widthwise reducing the longitudinal end of the slab by the sizing press reduction method to suppress the fish tail. Since the longitudinal central portion of the cast slab is rolled by a skewer roll by a method, high yield and productivity can be compatible.
On the other hand, if a two-step reduction as described in the above-mentioned Patent Document 4 is performed in order to increase the width reduction amount of the longitudinal direction end in the sizing press reduction method, seam wrinkles (he疵) may occur. When seam wrinkles occur, it is necessary to clean the portion where the wrinkles occur, such as by machining, and there is a problem that the yield is deteriorated. Furthermore, there is a problem that the temperature of the slab decreases because it passes through an extra step of etching, and it takes more time to heat the furnace than in the case where it is transported to the next step without maintenance, which hinders the productivity of the next step. The

  The present invention has been made in view of the above circumstances, and reduces the width dimension of a cast slab whose width dimension is determined by the mold dimensions of a continuous casting machine while suppressing the occurrence of seam flaws on the surface of the slab. It is an object of the present invention to provide a method of forming a cast slab that can be performed.

  The specific method of the present invention is as follows.

[1] A first aspect of the present invention relates to a first inclined portion which is narrowed toward the end in the longitudinal direction by press-forming the end in the longitudinal direction of the cast strip in the width direction; By forming a first parallel portion connected to the inclined portion and extending along the longitudinal direction, and further pressing the longitudinal end of the first parallel portion of the cast strip in the width direction, A method for forming a slab, comprising: forming a second inclined portion which is further narrowed toward the end in the longitudinal direction, and a second parallel portion connected to the second inclined portion and extending along the longitudinal direction. The first inclined portion is formed by pressing the ingot in the width direction thereof once or more with the first mold while changing the relative position in the longitudinal direction of the ingot and the first mold. And a first pressing step of forming the first parallel portion, and a longitudinal relative relationship between the cast slab and the second mold The second inclined portion and the second parallel portion are formed by pressing a part of the first parallel portion with the second mold in the width direction of the slab one or more times while changing the position And a second pressing step of forming a total width reduction amount R _α , which is a reduction amount of the first parallel portion in the first pressing step, and the second parallel portion in the second pressing step It is a slab forming method of pressing so that the relationship with the total width reduction amount R _β which is a reduction amount is R _α / R _β ≦ 0.7 or R _α / R _β関係 2.0.

[2] In the billet forming method described in the above [1], the first mold and the second mold may be the same mold.

[3] In the billet forming method described in the above [1] or [2], the method further includes a width rolling step of rolling the end portion in the width direction of the slab obtained by the second pressing step It is also good.

According to the present invention, the total width reduction amount R _α in the press for forming the first inclined portion and the first parallel portion and the press for forming the second inclined portion and the second parallel portion under the sizing press pressure Between the second inclined portion and the second parallel portion, the relationship between the total width reduction amount R _β and R _α / R _β ≦ 0.7 or R _α / R _β 2.02.0 It is possible to reduce the thickness of the thickness-increasing part (thickness-increasing cost).
As a result, in the sizing mill rolling after the sizing press pressure, it is possible to prevent the over-increasing of the thickness-increasing part from falling down, so it is possible to suppress the occurrence of seam flaws. Therefore, it is possible to provide a method for forming a slab that can reduce the width dimension of the slab whose width dimension is determined by the mold size of the continuous casting machine while suppressing the occurrence of seam flaws on the surface layer of the slab.

It is a front view showing an example of a skewer roll used by sizing mill rolling. It is a top view which shows the generation | occurrence | production location of a seam flaw in the surface layer of a slab. It is explanatory drawing of a mechanism in which a seam crack generate | occur | produces in the surface layer of a slab, (a) is a side view which shows the contact aspect of a slab and a scum roll, (b) is a contact aspect of a slab and a scoop roll FIG. It is a top view of the slab obtained by 1st press process S1 and 2nd press process S2. It is a schematic diagram for demonstrating 1st press process S1, Comprising: (a) is the 1st width pressure reduction in 1st press process S1, (b) is the 2nd width pressure reduction in 1st press process S1, (c) ) Shows a plurality of width reductions in the first pressing step S1. It is a schematic diagram for demonstrating 2nd press process S2, Comprising: (a) is the 1st width reduction in 2nd press process S2, (b) is the 2nd width reduction in 2nd press process S2, (c ) Shows a plurality of width reductions in the second pressing step S2. It is a schematic diagram for demonstrating "the maximum thickness of a board width end part." It is a schematic diagram for demonstrating "total width | variety rolling-down amount." It is a graph which shows the relation between R _α / R _β and the ratio of the maximum thickness increase to the slab thickness. (A) is a schematic diagram which shows the state which width-rolls a slab in the width-rolling process (sizing mill rolling) by a skewer roll, (b) is a top view which shows the slab reduced to the target width dimension is there.

The inventors of the present invention diligently studied about the phenomenon that seam wrinkles (heger wrinkles) occur in the cast slab. As a result, the following findings were obtained.
(A) When sizing press reduction is performed by two-step reduction as described in Patent Document 4 and thereafter sizing mill rolling is performed, the position shown in FIG. 2, that is, the width direction of the longitudinal end side of the slab Seam wrinkles on the surface of the edge.
(B) The generation position of the seam weir shown in FIG. 2 corresponds to the vicinity of the transition portion between the parallel portion and the inclined portion formed by the second stage reduction under the sizing press pressure.
(C) The vicinity of the transition portion is a portion where the amount of thickness increase that occurs when the widthwise end of the slab is subjected to a two-step reduction by the sizing press pressure is the largest.
(D) As shown in FIGS. 3 (a) and 3 (b), when there is a locally thickened portion at the widthwise end of the slab, the inclined surface of the caliber portion of the skewer roll when performing sizing mill rolling ( That it falls into contact with the weir and this is the cause of the seam weir that occurs in the position shown in FIG.
(E) Therefore, if it is possible to reduce the maximum thickness of the widthwise end of the slab to the height at which it does not contact the inclined surface of the caliber portion of the crucible roll under sizing press pressure, this falling is prevented in subsequent sizing mill rolling To avoid the occurrence of seam wrinkles.
(F) Furthermore, this seam weir occurs particularly when the first stage and second stage reductions in the sizing press are close, for example, when the first stage reduction = 200 mm and the second stage reduction = 200 mm. Be high.
In addition, conventionally, the reduction amounts of the first and second stages are made close to each other because the equipment load is uniform and the number of pressing times is small, which does not impair the productivity.

  Hereinafter, a method for forming a slab according to an embodiment of the present invention made based on the above-described findings will be described with reference to the drawings. In the figure, for the slab, the longitudinal direction (conveyance direction) of the slab is defined as X, the width direction as Y, and the thickness direction as Z.

  In the slab forming method according to the present embodiment, the slab 1 having the shape shown in FIG. 4 is formed by performing the first pressing step S1 and the second pressing step S2 as a sizing press pressure.

As shown in FIG. 4, the first inclined portion 11a, the first parallel portion 11b, the second inclined portion 12a, and the widthwise end portions of the cast slab 1 are directed from the longitudinal center to the longitudinal end portions. A second parallel portion 12b is formed.
More specifically, when the slab 1 is viewed in plan, the first inclined portion 11a, the first parallel portion 11b, the second inclined portion 12a, and the second parallel portion 12b formed in each of the four corners The billet 1 is formed to have a tapered shape toward both longitudinal ends.

The first inclined portion 11 a is formed to be inclined so that the width dimension gradually decreases from the longitudinal central portion (unrolled portion) of the cast piece 1 to the longitudinal end in plan view. The inclination angle θ1 of the first inclined portion 11a with respect to the longitudinal direction X may be less than 90 degrees, for example, 30 degrees.
The first parallel portion 11b is formed to extend in parallel with the longitudinal direction X while being continuous with the longitudinal direction end of the first inclined portion 11a in plan view.
The first inclined portion 11a and the first parallel portion 11b are formed by a first pressing step S1 described later.

The second inclined portion 12a is connected to the end of the first parallel portion 11b in the longitudinal direction in plan view and inclined so that the width gradually decreases from the first parallel portion 11b toward the end of the longitudinal direction. It is formed. The inclination angle θ2 of the second inclined portion 12a with respect to the longitudinal direction X may be less than 90 degrees, for example, 30 degrees. In addition, inclination-angle (theta) 1 of 1st inclination part 11a and inclination-angle (theta) 2 of 2nd inclination part 11b may not be the same.
The second parallel portion 12 b is formed to extend in parallel with the longitudinal direction X while being continuous with the longitudinal end of the second inclined portion 12 a in plan view.
The second inclined portion 12a and the second parallel portion 12b are formed by a second pressing step S2 described later.

Then, about the 1st press process S1 and the 2nd press process S2 of the billet molding method which concern on this embodiment, it refers to FIG.5 (a)-(c) and FIG.6 (a)-(c) below. explain.
Reference numeral 20 denotes a press die. The press die 20 has a trapezoidal shape in a plan view, and is connected to the inclined pressing portion 20a inclined with respect to the longitudinal direction X of the slab 1 and the inclined pressing portion 20a and in the longitudinal direction X of the slab 1 And a parallel pressing portion 20b parallel to each other.
The relative position between the mold 20 and the cast slab 1 in the longitudinal direction X can be changed by a mold moving mechanism or a cast slab transport mechanism (not shown). As a result, by driving the die 20 in the width direction Y at an arbitrary position in the longitudinal direction X of the cast slab 1, the cast strip 1 can be subjected to width reduction.

(1st press process S1)
In the first pressing step S1, the slab 1 is directed in the width direction Y by the mold 20 while changing the relative position of the slab 20 in the heated state obtained by continuous casting and the mold 20 in the longitudinal direction X The first inclined portion 11a and the first parallel portion 11b are formed by pressing once or more.
At this time, it is preferable that the slab 1 be press-formed in a state where it is heated to 1000 ° C. to 1300 ° C.

Specifically, first, as shown in FIG. 5A, the die 20 is disposed so as to face the widthwise end of the cast iron 1 in the longitudinal direction end side, and the width reduction of the cast iron 1 is obtained. Do. Thereby, the first reduction shape (that is, the shape corresponding to the inclined pressing portion 20a and the parallel pressing portion 20b of the mold 20) formed of the first inclined portion 11a and the first parallel portion 11b is formed on the cast slab 1.
At this time, when the desired width reduction amount can not be obtained by one press, the relative position of the cast piece 1 and the mold 20 in the longitudinal direction X may be fixed and pressed several times in a fixed state. The amount of one press is defined by the capacity of the press (maximum reduction load).

Next, as shown in FIG. 5 (b), the width reduction of the slab 1 is performed while changing the relative position between the slab 1 on which the above-described first reduction shape is formed and the mold 20 in the longitudinal direction X. I do.
The amount of pressure reduction at this time is set such that the amount of pressure reduction of the first parallel portion 11 b in the above-described first pressure reduction shape is maintained. Therefore, as shown in FIG. 5B, the length in the longitudinal direction of the first parallel portion 11a having the first pressure reduction shape is increased.
And as shown in FIG.5 (c), the 1st inclination part 11a and the 1st parallel part 11b are formed by repeating the relative movement of the slab 1 and the metal mold | die 20, and the width reduction several times. Be done.
In addition, the relative movement distance of one time of the mold 20 may be equal to or less than the dimension in the longitudinal direction X of the parallel pressing portion 20 b of the mold 20.

(Second press step S2)
In the second pressing step S2, while changing the relative position in the longitudinal direction X between the cast slab 1 on which the first inclined portion 11a and the first parallel portion 11b are formed in the first pressing step S1 and the mold 20, A second inclined portion 12a and a second parallel portion 12b are formed by pressing a part of the first parallel portion 11b in the width direction of the slab 1 one or more times with the mold 20.
At this time, it is preferable that the slab 1 be press-formed in a state where it is heated to 1000 ° C. to 1300 ° C.

Specifically, first, as shown in FIG. 6A, the mold 20 is disposed to face a part of the first parallel portion 11b formed in the first pressing step S1. Apply width reduction. Thereby, in addition to the first inclined portion 11a and the first parallel portion 11b, the second reduction shape (that is, the inclined pressing portion 20a of the die 20 and the second parallel portion 12a and the second inclined portion 12b) A shape corresponding to the parallel pressing portion 20b is formed.
At this time, as in the first pressing step S1, when the desired width reduction amount can not be obtained by one press, the relative position between the slab 1 and the mold 20 in the longitudinal direction X is fixed several times It is good to divide into and press. The amount of one press is defined by the capacity of the press (maximum reduction load).

Next, as shown in FIG. 6 (b), the width reduction of the slab 1 is performed while changing the relative position between the slab 1 on which the above-described second reduction shape is formed and the mold 20 in the longitudinal direction X. Do.
The amount of pressure reduction at this time is set such that the amount of pressure reduction of the portion corresponding to the second parallel portion 12b in the above-described second shape of pressure reduction is maintained. Therefore, as shown in FIG. 6 (b), the length in the longitudinal direction of the second rolling-down shape is increased.
And as shown in FIG.6 (c), the 2nd inclination part 12a and the 2nd parallel part are formed by repeating the relative movement of the metal mold | die 20, and the width reduction several times.
In addition, the relative movement distance of one time of the metal mold | die 20 should just be below the dimension of the longitudinal direction X of the parallel press part 20b.

In the slab forming method according to the present embodiment, the total width reduction amount which is the total width reduction amount R _α of the first parallel portion 11b in the first press step S1 and the reduction amount of the second parallel portion 12b in the second press step S2. The pressing is performed so that the relationship with R _β is R _α / R _β ≦ 0.7 or R _α / R _β 2.02.0.
This is based on the new findings of the present inventors that the maximum thickness of the plate width end (see FIG. 7) is largest when the width reduction amount of the first stage and the width reduction amount of the second stage are comparable. It is based.
In addition, "the maximum thickness of the plate width end portion" refers to a portion where the thickness is the largest among the plate width end portions of the slab 1 after the second pressing step (the plate width end portion of the slab 1 Means the thickness of the portion in the vicinity of the second inclined portion 12a in the first parallel portion 11b.
Moreover, "the total width | variety rolling-down amount" is the total amount of the amount of rolling down from the both ends of the width direction, as shown in FIG. That is, the total width reduction amount R _α in the first pressing step S1 is the total amount of the half width reduction amount W1 at one width direction end and the one width reduction amount W2 at the other end direction end. The total width reduction amount R _β in the two-pressing process S2 is the total amount of the half width reduction amount W3 at one width direction end and the one width reduction amount W4 at the other width direction end.

FIG. 9 is a graph showing the relationship between the “value of R _α / R _β ” and the “ratio of maximum thickness increase to slab thickness” when the total width reduction amount R _α + R _β is fixed at 500 mm. is there. In this case, the slab thickness at this time is the thickness before the sizing press reduction, that is, the thickness after continuous casting, and the thickness increase margin refers to an increase margin of the thickness from the slab thickness It is the thing of adding both sides).
That is, "the ratio of the maximum thickness increase to the cast thickness" means (maximum thickness of the plate width end-cast thickness) / cast thickness [%].
As shown in FIG. 9, it can be seen that when the value of R _α / R _β is 1.0 to 1.5, the ratio of the maximum thickness increase to the cast slab thickness is the largest. As the value of R _α / R _β becomes smaller than 1.0, the ratio of the maximum thickness increase to the cast thickness decreases, and as the value becomes larger than 1.5, the maximum thickness increase to the cast thickness The ratio of

As the maximum thickness of the plate width end decreases, the slab 1 is less likely to hit the inclined surface of the caliber portion 101 of the skewer roll 100 in the width rolling process S3 (sizing mill rolling) performed after the second pressing process S2, It also becomes difficult to occur. In addition, since the seam wrinkles are generated in a partial thickness increase portion and the shape of the caliber portion 101 is designed so that no seam wrinkles are generated in the steady portion (second parallel portion 12b), the thickness increase cost is If it is 20% or less of the cast slab thickness, it becomes difficult to generate seam flaws empirically. Therefore, the value of R _α / R _β is 0.7 or less, or 2.0 or more. Further, since no seam flaws occur when the thickness increase is 15% or less of the slab thickness, the value of R _α / R _β is preferably 0.38 or less, or 4.0 or more. The value of R _α / R _β is more preferably 0.30 or less, or 4.30 or more.

In the billet molding method according to the present embodiment, the first pressing step S1 and the second pressing step S2 by the above-described mold 20 are performed on both end portions in the longitudinal direction of the billet 1, as shown in FIG. Thus, the width rolling step S3 using the skewer roll 100 having the caliber portion 101 is performed in several times. Thereby, it is possible to obtain the slab 1 reduced to the target width dimension as shown in FIG. 10 (b) without generating seam flaws.
The width rolling step S3 is performed in several stages with a rolling amount in a range not exceeding the upper limit of the rolling load, and is formed into a predetermined width over the entire longitudinal direction X.
In addition, although the shape is designed so that the caliber part 101 of the skewer roll 100 may be optimized by cast slab thickness, it can respond now to the fluctuation | variation of a cast slab thickness to some extent.

  The slab 1 obtained in the width rolling step S3 is rolled into a steel plate of a predetermined thickness through rolling in the thickness direction (rough rolling, finish rolling).

  As mentioned above, although the specific example of this invention was demonstrated based on preferable embodiment, this invention is not limited to these illustrations. The present invention includes various modifications and alterations of the specific examples illustrated above.

For example, although the same mold 20 is used in the first pressing step S1 and the second pressing step S2 in the above embodiment, the first mold is used in the first pressing step S1 and the second pressing step S2 is used in the second pressing step S2. A second mold having a shape different from one mold may be used. In this case, the inclination angle θ1 of the first inclined portion 11a and the inclination angle θ2 of the second inclined portion 12a can be made different.
Further, for example, although two-step slab width press forming is performed in the above-described embodiment, three or more stage slab width press forming may be performed.
For example, in the above-mentioned embodiment, although the 1st press process S1 and the 2nd press process S2 are performed to the longitudinal direction both ends of slab 1, only the longitudinal direction one end of slab 1 performs the 1st press process S1. By performing the second pressing step S2, the first inclined portion 11a, the first parallel portion 11b, the second inclined portion 12a, and the second parallel portion 12b are formed only at one longitudinal end of the slab 1 It is also good.

The first pressing step and the second pressing step (sizing press pressure reduction) were performed on the slab having a width of 1700 mm and a thickness of 277 mm, in which the width in the longitudinal direction was 1200 mm under a two-step pressure. With respect to the slab after the second pressing step, a width rolling step (sizing mill rolling) was performed using a skewer roll having a caliber portion, and the presence or absence of occurrence of seam flaws in the obtained slab was observed.
The conditions of the first pressing step and the second pressing step in each experimental example and the evaluation results are shown in Table 1. The increase in thickness was obtained by measuring the height of the most increased portion after performing only the first pressing step and the second pressing step (sizing press pressure) under the same conditions as in each example. .

As shown in Table 1, according to Experimental Examples 1 to 6 in which R _α / R _β is 0.7 or less or 2.0 or more, the sheet width end of the most thickened portion in the cast slab after the sizing press The maximum thickness can be reduced, and a slab free of seam flaws can be obtained.
On the other hand, in Experimental Examples 7 and 8 in which R _α / R _β is 1.50 and 1.00, the maximum thickness of the plate width end of the most thickened portion in the cast slab after the sizing press is large. In the sizing mill rolling, the portion came in contact with the caliber portion of the scissor roll and fell down, and seam scum occurred.

DESCRIPTION OF SYMBOLS 1 slab 11a 1st inclination part 11b 1st parallel part 12a 2nd inclination part 12b 2nd parallel part 100 square roll 101 カ リ リ バ ー part

Claims (3)

By pressing the longitudinal end of the slab in the width direction, the first inclined portion shrinks toward the longitudinal end, and the first inclined portion is connected to the first inclined portion and extends along the longitudinal direction. Forming a first parallel portion, and further pressing the end portion in the longitudinal direction of the first parallel portion of the cast strip in the width direction to further reduce the width toward the longitudinal end portion A slab forming method comprising: forming a second inclined portion; and forming a second parallel portion connected to the second inclined portion and extending in the longitudinal direction,
The first inclined portion is formed by pressing the ingot in the width direction thereof once or more with the first mold while changing the relative position in the longitudinal direction of the ingot and the first mold. A first pressing step of forming the first parallel portion, and a part of the first parallel portion by the second mold while changing the relative position in the longitudinal direction between the cast slab and the second mold; A second pressing step of forming the second inclined portion and the second parallel portion by pressing the sheet in the width direction of the slab one or more times;
Have
The relationship between the total width reduction amount R _α which is the reduction amount of the first parallel portion in the first pressing step and the total width reduction amount R _β which is the reduction amount of the second parallel portion in the second pressing step is And R _α / R _β ≦ 0.7 or R _α / R _β 2.02.0. The method according to claim 1, wherein the first mold and the second mold are the same mold.   The method according to claim 1 or 2, further comprising a width rolling step of rolling an end portion in a width direction of the slab obtained by the second pressing step.

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